Researchers led by The University of Nottingham and Liverpool John Moores University conducted an experiment with 32 women and 35 men, asking them to rate the attractiveness of the opposite sex based on a list of qualities.

The list included attributes that were selfless such as 'he does the shopping for his elderly neighbour', and those that were considered neutral such as preferences for food.

The results showed that both sexes rated potential partners for a long-term relationship as more attractive when they were told that the person had invested in altruistic acts, such as caring for a sick relative or doing voluntary work in their community.

The study also found that those surveyed rated individuals significantly more attractive as potential long-term partners when they displayed helping behaviours.

However, this behaviour had a smaller effect on male attractiveness, and no significant effect on female attractiveness, when the same people were rated as potential partners for a short fling.

"At first glance, it's difficult to see how natural selection could favour behaviours that involve investing significant time and resources to help others at a cost to oneself," said Dr Freya Harrison, a Research Fellow in The University of Nottingham's Life Sciences Centre for Biomolecular Sciences, and senior author of the report.

"We now know that 'altruistic' helping can actually increase evolutionary fitness in various ways - people might preferentially help their relatives, with whom they share genes, or they might target their helping toward others who are likely to reciprocate in the future," Harrison said.

Harrison added that an additional factor that researchers have started to investigate is that 'altruistic' acts might make someone more attractive to the opposite sex, increasing their chances of having children and passing on their genes.

"This study adds to a growing body of research which tries to explain why nice guys (and girls) might not always finish last!" said Dr David Moore, Senior Lecturer in Psychology from Liverpool John Moores University.